As antitumor agents, pyrimidine fluoride-based compounds such as fluorouracil are currently used. However, among cancer patients, some (approximately 3% of Caucasian breast cancer patients) are inherently deficient in dihydropyrimidine dehydrogenase (hereinafter abbreviated as DPD), which is an enzyme involved in the metabolism of the compound in its decomposition pathway. It has been reported that, when a pyrimidine fluoride-based antitumor agent is administered to such a DPD-deficient patient, the compound is not metabolized and remains in the body, leading to side effects or possibly even to death (Biochim. Biophys. Acta 633, 400-409(1980))
In an organism, uracil and thymine are generally metabolized into dihydrouracil and dihydrothymine, respectively, through the action of DPD. However, DPD-deficient patients are known to fail to metabolize uracil and thymine and to excrete large amounts of unchanged uracil and thymine into the blood or urine, particularly uracil (Adv. Exp. Med. Biol., 253A, 111-118 (1989)). Accordingly, if uracil or thymine in blood or urine is assayed prior to administration of a pyrimidine fluoride-bases antitumor agent to cancer patients, DPD-deficient patients can be screened in advance. As a result, use of the antitumor agent can be discontinued or the dose of the agent can be reduced, to thereby avoid serious side effects.
Conventionally, methods for assaying uracil have been known, including a high-performance liquid chromatographic method (Journal of Chromatography B, 672 (1995), 233-239) and an immunoassay method making use of a monoclonal antibody for psuedouridine (Japanese Patent Publication (kokoku) 4-21479). However, the former method is disadvantageous in that the preparation of samples is cumbersome, imposes a heavy workload, and requires a significant level of skill. In addition, a long period of time is generally required for assaying a number of samples, and the high cost of measurement and other apparatuses make the method disadvantageous. In the latter method, the employed monoclonal antibody —an antibody used for diagnosing a progressive cancer —exhibits a reactivity with uracil of 30-40% and also a reactivity with pseudouridine as high as 95-99%. Thus, use of such a monoclonal antibody that has cross-reactivity with uracil and pseudouridine cannot distinguish DPD-deficient patients from non-deficient patients.
Under such circumstances, the present inventors previously found a monoclonal antibody which reacts strongly with uracil without cross-reacting with dihydrouracil—a metabolite of uracil in the organism—and with pseudouridine employed as a tumor marker (International Patent Publication WO 99/20748).
However, the above monoclonal antibody also reacts strongly with N-carbamyl-β-alanine, which is a metabolite of dihydrouracil and is contained in large amounts in normal urine, and has insufficient reactivity with uracil. Thus, use of the monoclonal antibody as a diagnostic agent for DPD deficiency is problematic.
Thus, an object of the present invention is to provide a monoclonal antibody having a higher specificity with uracil and thymine. Another object is to provide a hybridoma producing the monoclonal antibody. Still another object is to provide an immunochemical assay method which can correctly determine uracil and thymine contained in urine. Yet another object is to provide a diagnostic agent containing the monoclonal antibody for diagnosing DPD deficiency.